WASHINGTON (Reuters) - The National Transportation Safety Board and Boeing ( BA ) have not been able to determine who removed a door plug in a new 737 MAX 9 Alaska Airlines 737 MAX 9 that suffered a mid-air emergency in January, the board's chair said Tuesday.

NTSB Chair Jennifer Homendy told reporters Boeing ( BA ) needs to make significant improvements to its safety practices. "The safety culture needs a lot of work (at Boeing ( BA ))," she said. "It is not there from the evidence itself, from what you see in the interviews. There's not a lot of trust, there's a lot of distrust within the workforce."